For example, in an optical spectrum analyzer, there is used at least one slit mechanism in order to extract a required spectrum component from a dispersed incident light. The slit mechanism must be configured such that the width of the slit can be varied depending upon a spectrum component to be extracted, and if the slit width cannot be set with high accuracy, it is impossible to extract only a required spectrum component. That is, since a slit formed by the slit mechanism exercises an important influence on the resolving power (resolution) of an optical spectrum analyzer, it is necessary that the slit mechanism forms a slit having a required width with accuracy as high as possible.
Heretofore, there have been proposed various types of variable width optical slit mechanisms, and a prior art slit mechanism disclosed in, for example, Japanese Patent Application No. 08-264691 (refer to Japanese Patent Application Public Disclosure No. 10-111175) filed on Oct. 4, 1996 by the same applicant as that of the present application will be described with reference to FIGS. 6 to 8.
FIG. 6 is a front view showing the whole construction of a variable width optical slit mechanism a portion of which is shown in section, that is disclosed in the above-mentioned Japanese Patent Application No. 08-264691, FIG. 7 is a sectional view taken along a longitudinal direction (vertical direction) of the slit mechanism main body shown in FIG. 6, and FIG. 8 is a plan view showing a linear guide, slit forming members, and blocks that are taken out of the slit mechanism main body shown in FIG. 6. The illustrated variable width optical slit mechanism comprises the slit mechanism main body that includes various components or members for forming a slit having a required width, and a drive part that includes a pulse motor or stepper motor 26 for rotatively driving a feed screw 21 of the slit mechanism main body. The feed screw 21 will be discussed later on.
The slit mechanism main body comprises: a frame 23; a pair of slit forming members 11L and 11R; a pair of slit forming member supports 12L and 12R on which the slit forming members 11L and 11R are mounted respectively; a linear guide 13 that is constituted by a guide rail 15 of a generally rectangle in section mounted on the frame 23 at a predetermined position thereof in the horizontal direction, and a pair of carriages 14L and 14R movably supported on the guide rail in a straddle-type; blocks 18L and 18R that are mounted on the top surfaces of the supports 12L and 12R respectively; a feed screw 21 that is rotatably mounted on the frame 23 at a predetermined position thereof above the supports 12L and 12R in the horizontal direction; a pair of nuts 19L and 19R that are engaged with the feed screw 21; a pair of slide guides 22L and 22R that guide the nuts 19L and 19R such that while the nuts 19L and 19R are moved by revolution of the feed screw 21, they can move straight in the axial direction of the feed screw 21; and a spring 17 that gives to the pair of slit forming members 11L and 11R a force always energizing the slit forming members 11L and 11R to approach each other.
The supports 12L and 12R are long and narrow plate-like members each having a generally rectangular shape in plan in this example, and are disposed in such manner that the major sides thereof form substantially a right angle with the longitudinal direction of the guide rail 15. The bottom surfaces of the rear sides (the right side portions in FIG. 7) of the supports 12L and 12R are respectively mounted on the carriages 14L and 14R each having a generally square shape in plan in this example, and on the top surfaces of the rear sides thereof are mounted the blocks 18L and 18R, respectively. The slit forming members 11L and 11R are mounted on the bottom surfaces of the front sides (the left side portions in FIG. 7) of the supports 12L and 12R in such manner that their slit forming edges 11LE and 11RE each having a knife-edge shape are opposed to each other, the front sides of the supports 12L and 12R extending ahead of the carriages 14L, 14R and the frame 23. A slit of a required width through which a light should pass is formed between the slit forming edges 11LE and 11RE of the pair of slit forming members 11L and 11R. Further, FIGS. 6 and 8 show the state that the slit forming edges 11LE and 11RE of the pair of slit forming members 11L and 11R come into contact with each other and hence the width of the slit is zero (the state that any light is prevented from passing through the slit).
The pair of nuts 19L and 19R each engaged with the feed screw 21 have their internal threads one of which is a left-handed thread and the other of which is a right-handed thread so that when the feed screw 21 rotates, the nuts 19L and 19R are moved toward each other or away from each other. That is, when the feed screw 21 rotates in the clockwise direction, in this example, the left side nut 19L in FIG. 6 is moved leftward and the right side nut 19R in FIG. 6 is moved rightward (the nuts 19L and 19R are moved away from each other), and on the contrary, when the feed screw 21 rotates in the counterclockwise direction, the left side nut 19L is moved rightward and the right side nut 19R is moved leftward (the nuts 19L and 19R are moved toward each other). Of course, it may be arranged that when the feed screw 21 rotates in the clockwise direction, the left side nut 19L is moved rightward and the right side nut 19R is moved leftward, and when the feed screw 21 rotates in the counterclockwise direction, the left side nut 19L is moved leftward and the right side nut 19R is moved rightward. Further, it is constructed that the pair of nuts 19L and 19R has their top surfaces that are in contact with the bottom surfaces of the corresponding slide guides 22L and 22R, respectively, and as a result, the nuts 19L and 19R are prevented from rotating about the axis of the feed screw 21 thereby to move rectilinearly.
On the bottom surfaces of the pair of carriages 14L and 14R are formed respectively channel-like grooves adapted to straddle or mount the guide rail 15 so that the carriages 14L and 14R are movably put on the guide rail 15 in a straddle-type. Each of the carriages 14L and 14R has its one side that is considerably longer in length than the minor side of each of the supports 12L and 12R, and the supports 12L and 12R are mounted on the top surfaces of the carriages 14L and 14R at the remote side positions thereof opposed to each other, respectively. At the neighboring side positions opposed to each other on the top surfaces of the carriages 14L and 14R are mounted two fastening screws 16L and 16R each side position on both sides of the guide rail 15, respectively. Tension springs 17 are spanned between the opposed fastening screws 16L and 16R of the carriages 14L and 14R, respectively, and hence both the carriages 14L and 14R are always energized toward each other by the two tension springs 17.
The pair of blocks 18L and 18R is disposed along the longitudinal direction of the guide rail 15. Pushing portions 19La and 19Ra suspended respectively from the pair of nuts 19L and 19R abut against the opposed end surfaces of the blocks 18L and 18R, respectively, thereby to control the movement of the pair of carriages 14L and 14R toward each other. That is, since the pair of carriages 14L and 14R is always in pressure contact with the pushing portions 19La and 19Ra by the elastic forces of the two tension springs 17, as the pushing portions 19La and 19Ra move, the pair of carriages 14L and 14R also move.
Further, the feed screw 21 is rotatably supported by a pair of bearings 24 mounted to the frame 23, and one end thereof projecting to the outside from the frame 23 is coupled to the pulse motor 26 of the drive part through a coupling 25.
In the variable width optical slit mechanism constructed as mentioned above, setting (adjustment) of the width of a slit that is formed between the slit forming edges 11LE and 11RE of the pair of slit forming members 11L and 11R is effected by driving the pulse motor 26. For example, in case the slit forming members 11L and 11R in the state that the slit width is zero as shown in FIGS. 6 and 8 are separated to set a required slit width, the pulse motor 26 is driven to rotate the feed screw 21, for example, in the clockwise direction thereby to move the pair of nuts 19L and 19R away from each other. As a result, the pair of blocks 18L and 18R is pushed by the pushing portions 19La and 19Ra of the pair of nuts 19L and 19R, respectively, and the pair of carriages 14L and 14R move away from each other against the elastic forces of the two springs 17. Accordingly, a slit having a required width can be formed between the slit forming edges 11LE and 11RE of the slit forming members 11L and 11R.
Further, except for the pair of slit forming members 11L and 11R, each of pairs of the slit forming member supports 12L and 12R, carriages 14L and 14R, blocks 18L and 18R, nuts 19L and 19R, and slide guides 22L and 22R is constituted by two members having substantially the same shape and size with each other and disposed in axial symmetry.
Many of variable width optical slit mechanisms of this type are constructed such that an origin signal is generated when the width of a slit is zero. In the prior art described above, the pair of slit forming members 11L and 11R are used as both slit forming members and electrodes for generating an origin signal. For this reason, both of the slit forming members 11L and 11R are electric conductors made of; for example, a metal, and as shown in FIG. 8, terminals 27L and 27R are connected to the slit forming members 11L and 11R, respectively. These terminals 27L and 27R are connected to a signal source 28 through lead wires.
In such way, since the pair of slit forming members 11L and 11R are used as electrodes for generating an origin signal as well as slit forming members, in order to prevent these slit forming members 11L and 11R from being connected to the signal source 28 via, for example, the linear guide 13, the feed screw 21, the nuts 19, and the like, it is required that the slit forming members 11L and 11R are electrically insulated. Accordingly, in the prior art discussed above, the pair of slit forming member supports 12L and 12R for supporting the pair of slit forming members 11L and 11R are made of an insulation material, for example, an insulative synthetic resin or plastic, thereby to electrically insulate the pair of slit forming members 11L and 11R from other components or members.
As described above, the pair of slit forming members 11L and 11R are long and narrow plate-like members each having a generally rectangular shape in plan and is mounted on the corresponding carriages 14L and 14R of the linear guide 13 in a cantilever manner. Moreover, the slit forming member supports 12L and 12R are mounted on the portions of the supports 12L and 12R projecting respectively from the carriages 14L and 14R.
It cannot be said that the slit forming member supports 12L and 12R made of an insulation material (synthetic resin) are good in their temperature characteristic, and so there is a disadvantage that the dependence on temperature of a slit width formed by the pair of slit forming members 11L and 11R becomes large. In addition, since the supports 12L and 12R have an insufficient rigidity, there is a problem in their mechanical stability. As a result, the prior art variable width optical slit mechanism cannot form a slit with high precision.